Let's talk about the water cycle. First of all, there is no such thing as "New Water"! The water we have on the Earth right now is the same water that the dinosaurs drank. Fortunately, the Earth has a terrific system for recycling water called the water cycle. We also know it as the hydrologic cycle. The water cycle does a great job of cleaning up the water as it recycles it.
The water cycle has several steps in it. They are evaporation, condensation, and precipitation. Evaporation (D)is the process of liquid water changing into a gas called water vapor. Always remember, water vapor is INVISIBLE! Water molecules must gain energy before they can evaporate and that energy comes from the Sun. The Sun powers the water cycle. Once a water molecule gains enough energy, usually from the Sun, it can leap into the air and begin to float around. As the water molecules move around in the air, they can lose energy and cool off. When the water molecules cool off, they begin to stick to particles of dust, salt, and even smoke, and then each other. As they cool off, the molecules begin to condense.
Condensation (B)is the process of water vapor changing from a gas back into a liquid. Clouds are condensation. Clouds are NOT water vapor. Fog is a cloud that formed on or near the ground. Dew and frost are both forms of condensation. Dew and frost form in the early morning when it is very cool or cold. The water vapor in the air condenses on cool surfaces and forms the dew and if it is cold enough can freeze to form frost.
When you breathe on a window or a mirror, the fog you see is where the water vapor from your breathe condensed on the cool glass.
Water vapor is less dense than the atmosphere so water vapor will rise up into the sky. As water vapor gets higher and higher into the sky, it begins to cool off. When it gets cool enough it will begin to condense. Condensing water vapor forms tiny droplets of water. These tiny droplets form the clouds that we see. As they get cooler, the tiny droplets begin to stick together, growing larger and larger. When they get large enough, gravity actually pulls the droplets towards the Earth as precipitation.
Precipitation(C) is either a liquid or solid form of water that is falling back to the Earth. Precipitation can be either rain, sleet, snow, or hail. Remember, precipitation is made up of the tiny droplets that got large enough to fall back to the Earth. Snow is a collection of the droplets that froze as they stuck together, sleet is droplets of water that froze as they fell towards the ground, and hail forms during powerful thunderstorms.
OK, so far we have gotten the water up into the sky and now it is on its way back towards the ground. Now we need to get it back to some place where it can evaporate again. Well some of it can actually evaporate before it hits the ground, especially on hot days. Some of the precipitation that does hit the ground soaks(infiltrates)(K) into the ground where some of it gets absorbed by the roots of plants. The water that gets absorbed by the plants gets released back into the atmosphere as water vapor thru a process called transpiration(H). Transpiration releases water vapor sort of like our perspiration releases water vapor from our skin. Think sweat!!! A lot of the water that infiltrates into the ground makes its way down into the aquifer(F) where is forms groundwater. Groundwater can eventually wind up in the ocean but it can take thousands of years. Humans can really speed up the process of groundwater getting back into the water cycle though our use of wells for drinking water and irrigation. Some of the precipitation forms puddles and ponds which then evaporates rather quickly back into the atmosphere. A great deal of water forms the runoff that fills streams and rivers and quickly makes its way back to the ocean.
The ponds, rivers, lakes, and oceans are places where water can accumulate before it evaporates again. In the water cycle, these are known as reservoirs or accumulation(G). Now I don't know about you, but I don't usually drink out of ponds or rivers because I don't know what may have taken a bath in them lately. In fact, water from any of these sources can be unsafe for us to drink and we certainly can't drink ocean water, but we can drink rainwater. No matter how dirty a body of water is, the water vapor that evaporates is perfectly clean. ONLY the water evaporates! Salt, dirt, and anything else unpleasant gets left behind.
As water travels through the water cycle, it can also spend some time sort of waiting around between some of the steps. This waiting around can take place in the oceans, in rivers, trapped in snow, or even in aquifers as groundwater.
As we already learned, by far, most of the water on the Earth is found in the oceans, and as we know, ocean water is salty. Now almost all of the water in the water cycle winds up in the ocean and gets recycled from there. So a great question is why doesn't rain taste salty. Well, this goes back to that cleaning up part that I mentioned in the first paragraph. When water evaporates, only the water evaporates, the salt gets left behind in the ocean. Can you imagine what clouds would look like if mud, crud, and algae evaporated? You would not want to get caught out in the rain!
Well, that's about it for the water cycle. If we start with evaporation/transpiration, then comes condensation, next comes precipitation, and on and on forever!